ABSTRACT The work presented here focusses on developing adhesive by blending tannin and polyvinyl alcohol (PVA) in water. To furthermore enhance the properties crosslinking is carried by using boric acid at varying concentrations. Presence of free hydroxyl groups in PVA and tannin acts as a site for crosslinking reaction. The empty p orbital of trivalent boron atom attracts nucleophilic hydroxyl groups of PVA and tannin, hence are expected to form crosslinks. The interaction of boric acid with the blend was confirmed by FTIR spectra studies. The acidic pH favoured the reaction and its effects were observed by increase in viscosity and glass transition temperature (Tg). Films cased with the crosslinked blend demonstrated less hydrophilic behaviour from water contact angle test also increment in pencil hardness value and stress-bearing capacity. Adhesive performance properties like wet tack and time-dependent tensile lap shear strength on softwood and hardwood specimens were evaluated. The crosslinking-enhanced cohesion by reducing the free volumes between the chains and due to this, enhancement in tensile strength on bonded wood substrates was observed. Overall, it was found that the adhesive prepared by crosslinking PVA/tannin blend with boric acid is suitable for wood adhesive application.

中文翻译：

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硼酸对聚乙烯醇-单宁共混物的影响及其作为水性木材胶粘剂的应用

摘要 这里介绍的工作重点是通过在水中混合单宁和聚乙烯醇 (PVA) 来开发粘合剂。为了进一步增强性能，通过使用不同浓度的硼酸进行交联。PVA 和单宁中游离羟基的存在是交联反应的场所。三价硼原子的空 p 轨道吸引 PVA 和单宁的亲核羟基，因此有望形成交联。FTIR 光谱研究证实了硼酸与混合物的相互作用。酸性 pH 有利于反应，通过增加粘度和玻璃化转变温度 (Tg) 观察到其影响。涂有交联混合物的薄膜在水接触角测试中表现出较少的亲水性，铅笔硬度值和应力承受能力也有所增加。评估了软木和硬木样品的粘合性能，如湿粘性和随时间变化的拉伸搭接剪切强度。通过减少链之间的自由体积，交联增强了内聚力，因此观察到粘合木材基材的拉伸强度增强。总体而言，发现通过将 PVA/单宁混合物与硼酸交联制备的粘合剂适用于木材粘合剂应用。